P1258: MOLECULAR CYTOGENETICS CHARACTERIZATION OF CLASSICAL HODGKIN LYMPHOMA. ROL OF 9P24.1 (PD-L1/PD-L2) POLYSOMIES
Authors: M. García-Montenegro, M. Narbaitz, M. F. Metrebian, A. Pavlovsky, I. Slavutsky
Journal: HemaSphere (2022)

Background: Classical Hodgkin lymphoma (CHL) is characterized by scarce Reed-Sternberg/Hodgkin (RS/H) cells surrounded by a dense immune cell infiltrate belonging to the tumor microenvironment (TME). Chromosomal alterations on 9p24.1 (PD-L1/PD-L2) locus, especially amplifications and gains, are considered as recurrent abnormalities in RS/H cells as well as a potential prognostic and predictive marker of immunotherapy. Aims: To characterize genomic imbalances at 9p24.1 locus by FISH on formalin-fixed paraffin embedded primary diagnostic biopsies of CHL patients, in both RS/H and TME cells, and correlate them with histopathological, immunohistochemically and clinical parameters. Methods: A retrospective analysis of randomly chosen biopsies of patients with CHL enrolled in the GATLA LH05 study was performed. For FISH analysis, the SPEC CD274/PDCD1LG2/CEN9 probe (9p24.1) (ZytoVision, Germany) was used. In each patient, 50 RS/H and 100 TME cells were analyzed and the frequency of 9p24.1 alteration were determined. Nuclei with a target:control ratio ≥3:1 was defined as amplification (A), >1:1 but <3:1 as gains (G) and 1:1 as polisomy (P). According to the magnitude and percentage of cells with A, G and P, patients were divided in: AGP group (with A), GP-G-rich group (G>50%) and GP-P-rich group (P≥50%). Protein expression of PD-L1 was evaluated by immunohistochemistry (IHC) using anti-PD-L1/CD274 antibody clone RBT-PDL1 (BioSB, USA); the H-score modified (HSM) (range: 8-300) was applied. EBV integration was evaluated using LMP1 antibody clone CS1-4 (Cell Marque, Germany) as positive/negative. The study was approved by the Institutional Ethics Committee, in compliance with the Helsinki Declaration. Results: A total of 28 patients with CHL (14 males; mean age: 31 years, range: 18-54 years; early stages: 64.3%; advanced stages: 35.7%) were analyzed. All cases showed PD-L1/PD-L2 copy number alterations, with huge intratumoral heterogeneity, belonging 32% to AGP group, 36% to GP-G-rich and 32% to GP-P-rich. In addition to the A, the number of P were significantly different between groups (p<0.01). All cases showed PD-L1 expression; differences in the HSM mean between groups were observed: AGP: 266, GP-G: 123 and GP-P: 60 (p<0.01). Negative correlation between the HSM and the number of P for each group was found (p<0.01). No association with LMP1 expression or CHL histological subtype was observed. TME cells showed chromosome 9 (Ch9) monosomy in 100% of patients from the GP-P-rich group compared to 40% of the remaining cases. In relation with the clinical data, GP-P-rich group showed a higher mean age at diagnosis (38 years) than AGP and GP-G-rich groups (29 years) (p=0,019). In addition, GP-P group had higher frequency of advanced stage (p=0,035), extranodal involvement and B symptoms compared to the other groups, which showed association with localized stage and bulky disease. Interim PET scan after 3 cycles of ABVD (PET3) was positive (Deauville score 3-4-5) in 55.5% of cases with A compared to 26.3% of patients without A (Figure 1). Image:Summary/Conclusion: Our results confirm the high recurrence of 9p24.1 alteration in CHL, associated with highly intratumoral heterogeneity. In spite of the limited number of our series, we found differences in clinical parameters, PD-L1 protein expression and TME cells with Ch9 monosomy in GP-P-rich cases compared to the other groups. These findings suggest an important role for polysomies in the biologic characterization of CHL patients.